Genetics Problem Set #2

1. Hemophilia results from a recessive X-linked gene. Jill has hemophilia. She marries Bill, who has normal blood clotting. What proportion of their children are expected to have hemophilia?2. Red-green color blindness in humans is due to an X-linked recessive gene. A woman whose father is color blind possesses one eye with normal color vision and one eye with color blindness. Propose an explanation for this woman’s vision pattern.3. Red-green color blindness is an X-linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. If Bill and Martha marry, what types and proportions of children can they produce?4. The following two genotypes are crossed: Aa Bb Cc X+Xr x Aa BB cc X+Y, where a, b, and c represent alleles of unlinked autosomal genes and X+ and Xr represent X-linked alleles in an organism with XY sex determination. What is the probability of obtaining genotype aa Bb Cc X+X+ in the progeny?5. In the pearl millet plant, color is determined by three alleles at a single locus: Rp1 (red), Rp2 (purple), and rp (green). Red is dominant over purple and green and purple is dominant over green. Give the expected phenotypes and ratios of offspring produced by the following crosses.a. Rp1Rp2 x Rp1rpb. Rp1rp x Rp2rpc. Rp1Rp2 x Rp1Rp2d. Rp2rp x rprpe. rprp x Rp1Rp26. If there are five alleles at a locus, how many genotypes may there be at this locus. How many different kinds of homozygotes will there be?7. Allele A is epistatic to allele B. Indicate whether each of the following statements is true or false. Explain why.a. Alleles A and B are at the same locus.b. Alleles A and B may be located on different, homologous chromosomes.c. Alleles A and B may be located on different, nonhomologous chromosomes.8. A variety of opium poppy having lacerate leaves was crossed with a variety that has normal leaves. All the F1 had lacerate leaves. Two F1 plants were interbred to produce the F2. Of the F2, 249 had lacerate leaves and 16 had normal leaves. Give genotypes for all the plants in the P, F1, and F2 generations. Explain how lacerate leaves are determined in the opium poppy.9. In a type of plant known as a four o’clock, the allele for red flowers is incompletely dominant over the allele for white flowers, so that heterozygotes have pink flowers. What ratios of flower colors would you expect among the offspring of the following crosses:a. pink x pinkb. white x pinkc. red x redd. red x pinke. white x whitef. red x whiteg. If you specifically wanted to produce pink flowers, which of these crosses would be most efficient?10. When a yellow female Labrador retriever was mated with a brown male, half of the puppies were brown and half were yellow. The same female, when mated with a different brown male, produced only brown males. Explain these results.11. In mice, the Ay allele of the agouti gene is a recessive lethal allele, but it is dominant for yellow coat color. A second locus controls the deposition of color where C allows pigment and c does not. C is dominant to c. What phenotypes and ratios of offspring would you expect from the cross of a mouse heterozygous at the agouti locus (AyA) and also at the albino locus (Cc) to an albino mouse (cc) heterozygous at the agouti locus?12. In goats, a beard is produced by an autosomal allele that is dominant in males and recessive in females. We’ll use the symbol Bb for the beard allele and B+ for the beardless allele. Another independently assorting autosomal allele that produces a black coat (W) is dominant over the allele for white coat (w). Give the phenotypes and their expected proportions for the following crosses.a. B+B+Ww male x B+BbWw femaleb. B+BbWw male x B+Bbww femalec. B+B+Ww male x BbBbWw femaled. B+BbWw male and BbBbww female13. Shell coiling of the snail Limnaea peregra results from a genetic maternal effect. An autosomal allele for a right-handed shell (s+), called dextral, is dominant over the allele for a left handed shell (s), called sinistral. A pet snail called Martha is sinistral and reproduces only as a female. Indicate which of the following statements are true and which are false. Explain your reasoning in each case.a. Martha’s genotype must be ss.b. Martha’s genotype cannot be s+s+.c. All the offspring produced by Martha must be sinistral.d. Martha’s mother must have been sinistral.e. All of Martha’s brothers must be sinistral.14. You have in your possession three strains of phage, each carrying a single mutation that prevents the phage from infecting a bacterial cell and killing it by lysing it. When you try to infect bacteria with each strain individually and then plate the cells in agar Petri dishes, your plates are covered with bacteria. You want to see if any of the mutations are in the same gene, so you conduct a complementation test and co-infect your bacteria with two strains of phage. Your results:Plate 1: Phage A + Phage B = cleared regions representing bacterial lysis seenon the platePlate 2: Phage A + Phage C = bacterial growth with no cleared regionsa. Are A and B or A and C alleles of the same gene?b. Are B and C alleles of the same gene?